[ovs-discuss] Fwd: question regarding openflow flow table

Ben Pfaff blp at nicira.com
Thu Dec 16 16:05:26 UTC 2010

On Thu, Dec 16, 2010 at 8:00 AM, Haris Rotsos <cr409 at cam.ac.uk> wrote:
> I noticed using ovs-ofctl that openvswitch has 2 tables : hash with
> wildcard 0x000000 and classifier with wildcard 0x3fffff. My
> understanding is that the first table is used for exact matches flows,
> while the second is used for wilcarded flows. When I insert the
> wildcard flows in the switch, I notice that they are placed in the
> classifier table. Doesn't this has a performance penalty? The has hash
> table uses a hash function with seek time constant, while the
> classifier uses a linear lookup with linear seek time depending on the
> number of flows in the table.

If you're using Open vSwitch, then you are wrong that the classifier
uses linear lookup.  It does not.

If you have large numbers of wildcarded flows, recent versions of Open
vSwitch (from the Git repository) will have better performance than
older ones, because the classifier's performance has been improved.
They also report only a single table, but this is really not relevant
to performance.

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